1. Field of the Invention
The invention relates to an assembly and method, including a thin film membrane, and more particularly to an assembly using a thin film membrane which is used to humidify or dehumidify a sample gas or liquid.
2. Description of the Related Art
Previously known dryers have used hygroscopic ion exchange membrane tubes in a continuous drying process to selectively remove water vapor from mixed gas streams. Previous known membranes in such dryers have been formed as an extrudible desiccant in tubular form. A single tube, or a bundle of tubes 16 with a common header 18 as shown in Prior Art FIG. 11, is fabricated in a shell and tube configuration and sealed into an impermeable shell 10, which has a wet feed inlet 12 for the introduction of wet product and a dry product outlet 14. Bundles of the tubes 16, each having a wall thickness of between 3-7 mils, may be secured in place using a thermoset resin. A wet gas stream flows through the tubes, while a countercurrent dry gas stream, introduced through the dry purge inlet 20 and evacuated as wet purge gas through the wet purge gas outlet 22, purges the shell. Water vapor molecules are transferred through the walls of the tubing. As a result, the wet gas is dried, and the dry purge gas becomes wet as it carries away the water vapor. U.S. Pat. No. 5,160,511 to Lovelock shows one such so-called multi-tube dryer for drying a wet gas. The '511 patent discloses that tubing and membranes made of perfluoroethylene sulphonic acid under the tradename NAFION® by E. I. DuPont de Nemours have been used to add or remove water vapour from gas mixtures or from flowing streams of gas mixtures.
However, the above disclosed systems may be undesirable due to the cost of the extruded tubing used in such systems. Additionally, the thermoset resin used in the multi-tube devices reduces the chemical inertness of the tubes, as such resins have limited chemical resistance to many corrosive materials. Additionally, the multi-tube dryer end seals can crack when exposed to high temperatures and humidity as the tubing expands.
What is needed is an effective dryer that does not require extruded tubing, and as such, which can be fabricated into laminates or composites, rather than “bundles”. What is additionally needed is a device which is usable in a chemically inert fashion. What is further needed is a dryer device that reduces the fabrication, material and operating costs permitting the availability of low cost devices. What is additionally needed is a low cost dryer assembly for large process applications. What is further needed is a materials dryer useful in large flow process applications requiring maximum corrosion resistance.
Additionally, gas humidification systems using water permeable membranes are known. U.S. Pat. No. 5,996,976 to Murphy discloses the use of water permeable polymer materials, including perfluoronated sulfonic acid polymer membranes in the form of a tube, sheet or tubulated sheet, that can be saturated with water to allow evaporation of water into a gas stream passing over a water permeable member. One such procedure for using such tubing to humidify gases and hydrophobic liquids is additionally disclosed in Kertzman, ISA AID 75415 (1975).
An article by the present inventor, published in 1976 describes an apparatus for humidity generation, wherein liquid water at constant temperature is circulated through a tube pack contained in a shell, as with the device shown in FIG. 11. That article, entitled “Humidity Generator II”, refers to the energy input required to produce constant humidity. For example, in that article, a means of calibrating the Humidity Generator is described herein temperature sensors are placed at the water inlet and outlet of the tube pack. The inlet temperature measures the water temperature before evaporation of water, and the outlet temperature measures the decrease in temperature due to the latent heat of vaporization for a given mass of water. The water evaporated is calculated from a given formula.
What is further needed is a system for precisely humidifying gases and hydrophobic liquids.